Find Index of given fibonacci number in constant time | A simple C # program to find index of given Fibonacci number . ; if Fibonacci number is less than 2 , its index will be same as number ; iterate until generated fibonacci number is less than given fibonacci number ; res keeps track of number of generated fibonacci number ; Driver Code
using System ; class GFG { static int findIndex ( int n ) { if ( n <= 1 ) return n ; int a = 0 , b = 1 , c = 1 ; int res = 1 ; while ( c < n ) { c = a + b ; res ++ ; a = b ; b = c ; } return res ; } public static void Main ( ) { int result = findIndex ( 21 ) ; Console . WriteLine ( result ) ; } }